Heat transfer system for radioisotope generators

ABSTRACT

A device to dissipate heat from a radioisotope generator mounted in a separate housing which is designed to protect the generator from excessive water pressure. The device includes a pair of split elongate heat transfer cylinders positioned around the generator within the housing. One of the cylinders is in a contiguous relationship with the generator while the other cylinder is contiguous only to the housing. Both cylinders are in an end abutting relationship so as to provide a path for the flow of heat to the housing.

llnited States Patent [1 1 Hitchcock et al.

[ Mar. 27, 1973 [54] HEAT TRANSFER SYSTEM FOR RADIOISOTOPE GENERATORS[75] Inventors: Robert D. Hitchcock, Ventura; Gene P. McMahan, Oxnard,both of Calif.

[73] Assignee: The United States of America as represented by theSecretary of the Navy 221 Filed: Mar. 5, 1971 211 Appl.No.:121,327

[52] US. Cl. ..165/47, 165/185, 136/202,

250/106 R, 250/108 R [51] Int. Cl. ..F28f 13/00 [58] Field of Search..165/47, 80, 185; 310/3 R;

[56] References Cited UNITED STATES PATENTS Kaufman et al. ..l65/80 X2,935,549 5/1960 Woods ..l65/80 X 3,193,610 7/1965 Worden, Sr.....l65/80 X 3,262,820 7/1966 Whitclaw ..l36/202 3,586,100 6/1971 Yasudaet al.. ..165/80 Primary Examiner-Albert W. Davis, Jr. Attorney-RichardS. Sciascia, Q. Baxter Warner and Gayward N. Mann [57] ABSTRACT 3Claims, 5 Drawing Figures \lllllilt PATENTEDHARZHHH 722,579

HEAT TRANSFER RINGS FIG. I

\HHHH/ EXPANSION RING FIG 4 FIG. 3

HEAT SINK (OCEAN) AT 0 TEMPERATURE T HEAT-TRANSFER MEDIUM, TWO

' BUTT-CONTACT ALUMINUM SPLIT v F CYLINDERS, 0F RADlUS,l2.2cm

ROBERT D. HITCHCOG GENE F. McMAHAN INVENTORS HEAT TRANSFER SYSTEM FORRADIOISUIOPE GENERATORS STATEMENT OF GOVERNMENT INTEREST The inventiondescribed herein may be manufactured and used by or for the Governmentof the United States of America for governmental purposes without thepayment of any royalties thereon or therefor.

BACKGROUND OF THE INVENTION 1 Field of the Invention.

This invention relates to devices for dissipating heat from a heatgenerating source such as a submerged radioisotope generator. Moreparticularly the invention relates to devices for removing waste heatfrom such generators which are enclosed in a protective housing and inan underwater environment.

2. Description of the Prior Art.

Radioisotope power devices utilize the heat generated by radioactivematerial to produce electricity. However, all thermoelectric devicesmust conduct waste heat to the surrounding area at a rate high enough tokeep the temperature of such devices below a specified limit. Otherwisethe heat will not be rejected fast enough to maintain a necessarytemperature difference between the hot and cold sides of thethermoelectric device. This condition results in insufficient poweroutput.

When the radioisotope power device is enclosed in a separate housing,the problem of heat dissipation is even more critical unless the wallsof the housing are in direct contact with the outside surface of thedevice.

In many prior structures the contact between a power device or generatorand the housing is accomplished by the employment of small copperspheres in the annular space between the porous device and the housing.An inherent disadvantage of such a method to remove waste heat is thatthe small spheres often become lodged in the O-ring grooves which maycause a seal leak in the event the power device is used'in an aqueousenvironment. Another disadvantage is the tediousness involved in packingthe copper spheres; also internal electrical connections must beprotected from them.

SUMMARY OF THE INVENTION STATEMENT OF THE OBJECTS OF THE INVENTIONAccordingly it is an object of the present invention to provide aninexpensive device to dissipate waste heat from a radioisotope generatorenclosed in a separate housing.

Another object of the present invention is to provide a reliable meansof transferring waste heat from a radioisotope generator into anoceanographic housing which is in direct contact with water.

Other objects, advantages and novel features of the invention willbecome apparent from the following detailed description of the inventionwhen considered in conjunction with the accompanying drawings wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a schematic drawingpartially cut away showing the heat transfer cylinder in position withina protective housing.

FIG. 2 is an enlarged section along the line 22 of FIG. 1.

FIG. 3 is an enlarged view showing the detail of the expansion wedge andscrew.

FIG. 4 is an end view of one of the heat transfer cylinders showing thesplit therein.

FIG. 5 is a schematic representation of the heat transfer processevolving from operation of the present invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Most radioisotope generators aredesigned for operation in the open air since they will dissipate heat ata suflicient rate as long as the outer surface of the generator is incontact with room-temperature air. However, in the event the generatoris enclosed in a protective housing, waste heat cannot be dissipatedfast enough and accordingly the electrical power output is too low. Sucha housing might be employed for a mu]- titude of purposes including theprotection of the generator from excessive water pressure in the eventthe generator is placed in a deep ocean environment.

Referring now to the drawing, the invention includes a firsttransversely split cylinder 12 which encompasses the generator 10 and iscontiguous therewith. A second transversely split cylinder 14 is alsopositioned around the generator but contiguous with the inside surfaceof housing 16 and in butting relationship with one end of the firstcylinder 12 as shown in FIGS. 1 and 2.

In placing cylinder 12 in position, it is first expanded slightly by useof a wedge assembly 18 (FIG. 3) including opposed tapered shoulders20-21. After emplacement over one portion of the generator 10 the wedgeassembly 18 is released and removed and through its own elasticity thecylinder 12 contracts to fit firmly onto the exterior surface of thegenerator 10.

The generator 10 and its tightly fitting contiguous cylinder 12 are theninserted into a water tight housing 16. Thereafter, the second cylinder14 is positioned in place about the generator 10 and within the housing16 with its inner end abutting one end of cylinder 12. The wedgeassembly 18 is then actuated to expand split ring 14 into close contactwith the inside wall of housing 16. The wedge assembly 18 employed inthe expansion process remains in the tightened position to ensure thatcylinder 14 remains firmly in contact with the inside wall of housing16.

It is pointed out that both cylinders 12 and 14 are each preferablyconstructed of aluminum due to the ease in which this metal conductsheat. However, other suitable substances may be used as required.

A theoretical analysis of the operation of the invention is illustratedby the schematic shown in FIG. 5. In calculating the temperaturedifference existing between the radioisotope generator 10 and the heatsink, which could be the ocean if the generator were positioned on theocean floor, and into which the thermal energy is conducted at the samerate it is produced at the surface of the generator 10, the followingequation may be used:

T2 T1 where Q 30 joules/sec.

L= 17 cm K 0.5 calorie. cm/sec. cm c (thermal conductivity of aluminum)A (211) (12.2) (1.27) 97.3 cm therefore:

T T C This figure indicates that the outside temperature of thegenerator 10 need be only 2.5 C above the heat sink temperature toreject heat at the required rate of joules/sec. Accordingly if the heatsink were ocean water at a depth of 6,000 feet where such radioisotopegenerator is expected to be positioned, the temperature is about 2 C,the generator surface will be maintained well below a satisfactory roomtemperature.

A modification of the invention is to vary the configuration of thermalcontact between two split cylinders l2 and 14. Another modificationwould be to use a third unit between the first and second splitcylinders 12 and 14 respectively. However, both of these modificationswould require tapering th'e split cylinders at their contacting surfaceswhich makes assembly difficult and may cause damage to the housing 16.

Obviously many modifications and variations of the present invention arepossible in the light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims the inventionmay be practiced otherwise than as specifically described.

We claim:

1. A device to dissipate heat from a radioisotope generator which isenclosed in a separate protective housing comprising:

a first elongate heat transfer cylinder positioned around said generatorand contiguous thereto, and

a second elongate heat transfer cylinder also enclosing said generatorbut contiguous to the housing,

said first and second cylinders both being in an abutting relationshipalong the contiguous end wall portions, said heat transfer cylindersadapted to satisfactorily conduct heat to the exterior heat sink whenthe generator temperature is not less than 25 C above the heat sinktemperature.

2. The heat dissipation device as defined in claim 1 wherein both thefirst and second heat transfer cylinders are transversely split toensure firm contact with the generator and the housing.

3. A device to dissipate heat from a heat generator enclosed in aprotective housing as defined in claim 1 wherein:

a wedge assembly is positioned adjacent said second cylinder to maintainthe expanded condition of said cylinder and insure contact thereof withthe housing.

1. A device to dissipate heat from a radioisotope generator which isenclosed in a separate protective housing comprising: a first elongateheat transfer cylinder positioned around said generator and contiguousthereto, and a second elongate heat transfer cylinder also enclosingsaid generator but contiguous to the housing, said first and secondcylinders both being in an abutting relationship along the contiguousend wall portions, said heat transfer cylinders adapted tosatisfactorily conduct heat to the exterior heat sink when the generatortemperature is not less than 2.5* C above the heat sink temperature. 2.The heat dissipation device as defined in claim 1 wherein both the firstand second heat transfer cylinders are transversely split to ensure firmcontact with the generator and the housing.
 3. A device to dissipateheat from a heat generator enclosed in a protective housing as definedin claim 1 wherein: a wedge assembly is positioned adjacent said secondcylinder to maintain the expanded condition of said cylinder and insurecontact thereof with the housing.